Integrated circuit (IC) chips are enclosed in plastic packages that provide protecting against damage and environmental contaminants, and enable electrical of the chip to other circuits on a printed circuit board. Packaging IC chips has involved the placement of a chip on a flexible board where following adhesion of the chip to the board and wire bonding to connect the leads from the chip to the terminals on the board, an encapsulant is flowed over the chip and board to form a sealed package.
Plastic encapsulation of semiconductor devices by transfer molding is a conventionally used technique. Typically, a pre-encapsulated die unit is placed in a mold having top and bottom cavity molding plates. The lower molding plate has a constricted channel or mold gate along one side of the plate, and the encapsulation material, typically a thermoplastic or thermosetting material, enters through the mold gate and flows under and then over the IC chip to cover the electrical leads. The mold gate limits the flow rate and injection velocity of a molding compound into the cavity. The encapsulation material is then cured to harden it. In devices having a ball grid array (BGA) on one side of the substrate, the molding process is conducted so that the ball grid array connections are not covered by the molding compound during the encapsulation process.
The assembly process flows of standard BOC BGA packaging techniques are set-up for conventional IC chips having a bond pad layout arranged in a column down the center of the chip. Such packaging techniques cannot accommodate the assembly of die packages that do not utilize a standard wire bond slot and bond pad layout.
Currently, a semiconductor chip having a non-standard bond pad layout is packaged in a chip-on-board (COB) ball grid array (BGA) package. A disadvantage in using a COB BGA packaging technique is the use of long wires for connecting the bond pads in the center of the die to contacts on the underlying substrate, which are prone to damage. Another drawback is the resulting larger package size, which is needed to allow sufficient space for the wire bond connections.
In view of these and other deficiencies in conventional methods for fabricating BGA packages, improvements in fabrication methods for BOC BGA packages are needed.